Method of manufacturing a glass ceramic material which is resistant to sodium vapour

ABSTRACT

A method of manufacturing a glass ceramic body which is resistant to sodium vapor at a high temperature, comprises: shaping the body from a glass prepared by melting a mixture consisting of a composition in % by weight within the limits CaO 24-50, Al2O3 35-57.5, MgO 0-12, BaO 0-16, Y2O3 0-10, B2O3 0-9, ZrO2 0-17.5 and Li20 0-13, heating the body for 30 to 120 minutes at a temperature between 700* and 900*C, then for 0 to 120 minutes between 900* and 1000*C. then for 60 to 360 minutes at a temperature between 1000* and 1200*C.

United States Patent [191 Plesslinger et al.

[ Dec. 16, 1975 METHOD OF MANUFACTURING A GLASS CERAMIC MATERIAL WHICH IS RESISTANT TO SODIUM VAPOUR Inventors: Gertraud Agnes Anna Plesslinger,

Eindhoven, Netherlands; Frank Berthold; Erwin Roeder, both of Aachen, Germany Assignee: U.S. Philips Corporation, New

York, N.Y.

Filed: Nov. 18, 1974 Appl. No.: 524,703

Related U.S. Application Data Continuation of Ser. Nos. 340,218, March 12, 1973, abandoned, and Ser. No. 813,029, April 3, 1969, abandoned.

Foreign Application Priority Data Apr. 10, 1968 Germany 1771143 U.S. Cl 65/33; l06/39.6 Int. Cl. C03C 3/22 Field of Search l06/39.6; 65/33 References Cited UNITED STATES PATENTS 11/1961 Kreidl et a1. 106/39.6

3,163,513 12/1964 Brown 65/33 3,281,309 10/1966 Ross 106/39.5

3,441,421 4/1969 Sarver et a1 106/39.5

3,469,729 9/1969 Grekila et a1. 106/47 X 3,635,739 l/l972 MacDowell et al l06/39.6

Primary Examiner l-ielen M. McCarthy Attorney, Agent, or Firm-Frank R. Trifari; George B. Berka ABSTRACT 900 and 1000C. then for 60 to 360 minutes at a temperature between l000 and 1200C.

2 Claims, N0 Drawings METHOD OF MANUFACTURING A GLASS CERAMIC MATERIAL WHICH IS RESISTANT TO SODIUM VAPOUR ceramic material manufactured by said method, or in which the envelope itself consists wholly or partly of said glass ceramic material. I

Densely sintered polycrystalline aluminium oxide, (U.S. patent specification No. 3,026,210), consists at least of 99.5% of A1 0 It istranslucent, gas-tight and has an excellent resistance to the action by sodium vapour up to very high temperatures. This material is therefore used as an envelope for high pressure sodium vapour discharge lamps.

The sealing of said lamps and the sealing-in of the electrodes wasnot so simpleup till now. It was proposed inter alia (U.S. patent specification No. 3,281,309.) to use for this purpose melted eutectic mixtures on the basis of alkaline earth oxide and A1 0 which upon solidification produce a vitreous crystalline product. The crystalline phases in most of the compositions of this type are formed spontaneously and rapidly, so uncontrolled. As a result of this the mechanical rigidity and the gas-tightness of the resulting connection is strongly reduced. Actually, said material can only be useful as a cement and is unfit for the manufacture or rather large bodies.

In manufacturing sodium vapour discharge lamps it was so far necessary to use terminating or inserting members of densely sintered polycrystalline aluminium oxide. Theresult of this is that due to the matching'of the coefficients of expansion, the metal must consist of niobium which has the drawback that sealing together has to be carried out in a rare gas.

4 According to the method "of the invention, a glass ceramic material is manufactured 'which is resistant to C210 24 50 A1203 3s 57.5

MgO 0 12 12,0 0 9 B203 zro up 2:0 0 17,5 3 20 is first heated for to 120 minutes at a temperature between 700 and 900C, then from 0 to 120 minutes between 900 and 1000C and finally for 60 to 360 minutes between l000 and 1200C.

The resulting glass ceramic material which is finely crystalline has a sodium vapour resistance, as compared with glass of the same composition, which is satisfactory up to temperatures which are approximately 200C higher, so :to approximately 900C. For an envelope .of a high pressure sodium vapour discharge lamp it is not yet suitable. On the other hand, it may be used as an envelope when medium pressures are used. A number of glass. ceramic materials within the above range of compositions have a translucency which is comparable to that of densely sintered aluminium oxide. They are suitable for being processed, for example, to tubular bodies by means of the extrusion method, which is described in the British patent application Ser. No. 48,318/68 (U.S. Appl. Ser. No. 765,671 now abandoned) which have not yet been laid open to public inspection.

According to a preferred embodiment of the method according to the invention, a glass which is obtained 'by melting amixture of the composition in by weight calculated as an oxide, within the limits.

CaO 30 50,

ZrO

is first heated for 30 to 120 minutes at a temperature between 700-and 900C, then for 30 to 120 minutes between 900 and 1000C, and finally for 60 to 240 minutes between l000 and 1200C.

The treatment in three stages, that is to say including a treatment at a temperature between 900 and 1000C between the formation of nuclei and the nuclei growth reduces the danger of the formation of cracks in the material considerably.

In manufacturing high pressure sodium vapour lamps, having an envelope of densely sintered polycrystalline aluminium oxide, the glass ceramic material which is manufactured according to the invention presents the possibility of a much simpler sealing than the 5 one used so far. 7

FIG. 1 shows a known sealing. In this Figure, reference numeral 1 denotes the tubular envelope of densely sintered aluminium oxide, in which an annular member of the same material is provided in a clamping 0 manner at either end. The ring 4 likewise consists of the same material. Niobium is used as an electrode lead-in member 2, while the two rings 5 consist of a compressed glass powder mixed with a binder. The glass has, for example, the composition (in by weight): CaO 38.8; A1 0 45.6; MgO 5.2; BaO 8.7 and E 0 1.7, according to the British patent application Ser. No. 17.827/68 (U.S. Appl. Ser. No. 720,302 now abandoned). Upon heating, the binder burns away and forms a vacuum-tight connection between the envelope and the elctrode lead-in member.

FIG. 2 shows how the sealing with the material according to the invention is carried out much simpler. According to this method the plug of glass 7 which consists of one assembly is converted, after sealing-in, by a suitable thermal treatment into the glass ceramic material according to the invention. In this method of sealing the electrode lead-in member 6 may consist, for example, of molybdenum which is much cheaper.

In carrying the invention into effect it has been found that in the first phase of the thermal treatment finely divided nuclei, for example, in the formof 3 CaO.B O segregate in the glass. During the further thermal treatment the compound CaO.Al O which is excellently resistant to the action by sodium vapour crystallizes on said nuceli. Decisive of a suitable glass ceramic material is the choice of the composition and of the temperature program since in addition to CaO.-A1 the phase 12 CaO. 7 A1 0 which is very poorly resistant to the action by sodium vapour may also be separated.

The material obtained according to the invention cannot only be used as a sealing material for high pressure sodium lamps or for .medium pressure sodium lamps but also for other high load lamps.

In order that the invention may readily be carried into effect, it will now be described in greater detail with reference to a few examples. The compositions summarized in the table in by weight are melted from a mixture which contains calcium carbonate, aluminium oxide, boric acid, and, if required, magnesium carbonate, barium carbonate, zirconium oxide and yttrium oxide. Rods drawn from the melt are first heated at a temperature betwen 750 and 850C for 2 hours. The temperature is then raised at a rate of 4 to 5C per minute to 950C and kept at this value for 1 hour. The temperature is then increased once again at a rate of 4 to 5C. per minute to ll00C, kept at the last-mentioned temperature for 2 to 4 hours, and finally The sodium resistance is very good for all samples after a treatment at 850C for 48 hours. In the samples 1', 2 and 6, such a'load at 950C causes hardly any attack.

What is claimed is:

' l. A method for manufacturing a translucent glass ceramic body shaped of a glass produced by melting a mixture consisting of a composition in percentage by weight calculated as an oxide within ranges C210 50 A1203 55 MgO 2- 7 BaO 4- 16 17,0 0-10 B203 3-9 comprising devitrifying said glass body by heating it at temperatures between 700 and900C for time periods between 30 and 120 minutes to form 3 CaO.B O nuclei; then heating said body to a temperature between 900 and l000C and maintaining said temperature between 900 and l000C for a time period of 30 to 120 minutes, then heating said body to a temperature between l000 and 1200C and maintaining said temperature between l000 and 1200C for a time period between 60 and 240 minutes to crystallize CaO.Al O compound on said nuclei, said compound having a high resistance to the action of sodium vapor at high temcooled in air to room temperature. 30 peratures, and finally cooling Said y- Table.

. Composition by weight. Nr 1 2 3 4 5 6 7 8 9 10 11 12 C210 37,2 38,0 36,3 34,5 36,7 36,8 47,9 46,2 34,4 34,5 29,3 41,8 A1 0 43,4 44,4 42,3 40,4 40,4 43,0 43,6 1 46,9 40,2 50,3 46,7 52,0 MgO 4,9 2,8 2,6 2,5 2,7 5,9 4,5 BaO 8,3 1 8,5 8,2 7,9 8,3 8,2 15,3 13,0 6,2 6,3 6,0 5,7 6,1 6,1 8,5 6,9 5.6 Zrc)2 4,6 9,0 15,2 16,1 4,2 v 0, 5,8 1.1 0 2,0

, g 2. A method as claimed in claim 1, wherein heating v a said body to temperatures between 900 and l000C The phases 3 CaO.B O and CaO A1 0 can be deand between l000 and 1200C comprises temperature tected in an X-ray diffraction pattern in the final prodincreases at rates between 4 and 5C per minute. uct. The phase 12 CaO. 7 A1 0 is present in traces. 

1. A METHOD FOR MANUFACTURING A TRANSLUCENT GLASS CERMAIC BODY SHAPED OF A GLASS PRODUCED BY MELTING A MIXTURE CONSISTING OF A COMPOSITION IN PERCENTAGE BY WEIGHT CALCULATED AS AN OXIDE WITHIN RANGES
 2. A method as claimed in claim 1, wherein heating said body to temperatures between 900* and 1000*C and between 1000* and 1200*C comprises temperature increases at rates between 4* and 5*C per minute. 